Jason was a hero in Greek mythology, the leader of the Argonautic Expedition in the quest of retrieving the Golden Fleece. He was the son of the king of Iolcus, Aeson, but it is not certain who his mother was; various names appear in different sources as his mother.

When Jason was still a baby, his half-uncle Pelias, vying for the throne of Aeson, killed all of Aeson's children, and overthrew Aeson; however, he failed to kill Jason. The baby was sent to the centaurChiron, who nurtured him to adulthood. Pelias, in the meantime, consulted an oracle that told him to be careful of a man with one sandal. Jason, a grown man, returned to Iolcus to attend some games held by Pelias in honour of the god Poseidon; during his travel, he lost one of his sandals in the river Anauros while helping a disguised Hera to cross. Hera secretly blessed Jason at that point. Jason appeared in front of Pelias, asking for the throne as the rightful heir of Aeson, but Pelias gave him the quest to bring the Golden Fleece in order to step down from the throne.

Jason started creating a party of heroes, who were collectively called the Argonauts, after the name of Jason's ship, Argo. The Golden Fleece was located in the mythical region of Colchis that would take a long time to reach. After the Argonauts set sail, they first reached the island of Lemnos. There, all the women of the island had killed their husbands after a curse that had been afflicted on them by the goddess Aphrodite, because she was not properly worshipped. The Argonauts stayed for a while there, sleeping with the women of the island and creating a new race, called Minyans.

Their next stop after Lemnos was the land of the Doliones, where they were warmly greeted. They were told there were supplies to be found beyond Bear Mountain, where a mythical race of giants called Gegeines lived. While the Argonauts were looking for supplies, the Gegeines attacked the ship; Heracles, who participated in the expedition, managed to kill many of them before the rest of the Argonauts came and pushed the giants back. At night, they set sail but a mistake caused them to land back on the island, where the Doliones, thinking they were enemies, attacked them; in the battle that followed, many Doliones were killed. In the following day, the remorseful Argonauts held funerals for the slain.

They then went to Thrace, where the kingdom of King Phineus was being plagued by the Harpies. These monsters were sent by Zeus to steal food every day. Jason helped the king and killed the Harpies on their next attack. Phineus, grateful for Jason's help, told the Argonauts where Colchis lay and how to pass through the Symplegades, the Clashing Rocks. These were huge rock cliffs that would move and crush anything that passed between them. Phineus told Jason to release a dove and see if it would make it through, an omen for what would happen to the ship. The dove successfully passed, losing only a few tail feathers; so, when the ship travelled through the rocks, only minor damages were caused at the stern of the ship.

Jason and the Argonauts eventually reached Colchis, where they were welcomed by King Aeetes. The Golden Fleece was in the possession of the king, gifted to him by Phrixus when he arrived there on a flying golden ram. Aeetes said he would give the fleece to Jason if he successfully completed three tasks. Jason despared by his quests. Hera, favouring him, convinced Aphrodite and Eros to make Medea, Aeetes' daughter, to fall in love with Jason and help him in the tasks. The first task was to plow a field using Khalkotauroi, fire-breathing oxen; Medea gave Jason an ointment that protected him from the fire. The second task was to sow dragon's teeth in the field, causing an army of stone warriors to appear. Jason was forewarned by Medea, and following her advice, threw a rock into the army. The soldiers, not knowing who had thrown the rock, killed each other. The third task was to take the Golden Fleece from a sleepless dragon. A sleeping potion, provided by Medea, was enough for Jason to overcome the dragon and take the Golden Fleece.

After retrieving the fleece, Jason and the Argonauts left, and Medea joined them. Aeetes tried to follow them, but Medea killed her brother and threw his pieces into the sea, causing Aeetes to stop and retrieve them. Zeus, angry at Medea's act of killing her brother, caused a number of storms on their way back. To redeem themselves, they stopped at the island of Aeaea, where the nymph Circe lived to be purified. They then went on. On their voyage, they also met the Sirens that caused ships to crash onto the reefs, as their captivating voices mesmerised the crews; Orpheus, however, played the lyre and completely covered their voices, thus managing to evade the ill fate. Near Crete, they met Talos, a giant bronze man, who guarded the island and threw stones at anyone approaching. Medea cast a spell on him and they managed to remove the plug that kept Talos' ichor (the divine blood) in his single vein. Thus, he bled to death.

The Argonauts eventually managed to return to their home. Jason found his father Aeson at a very old age, and asked Medea to transfer some of his life to his father. Medea gave a few more years to Aeson, without removing them from Jason, but by infusing Aeson's blood with magical herbs. Pelias' daughters asked her to do the same for their father; Medea tricked them into killing him instead. As a result, Pelias' son exiled Jason and Medea.

The couple went to Corinth, where Jason fell in love and was engaged with Creusa. Medea, infuriated, confronted Jason, but he ignored her. As a revenge, Medea killed Creusa by giving her a dress that stuck on her and put her on fire; her father Creon was also burned trying to save his daughter. Medea then killed her sons that she had with Jason, fearing he would kill them as retaliation. She then abandoned Jason, flying to Athens on a dragon chariot sent by her grandfather, the sun god Helios.

Years later, Jason managed to reclaim the throne of Iolcus with the help of his friend, Peleus. However, he remained lonely, having lost the favour of Hera after breaking his vows to Medea. He died while sleeping under the stern of his ship Argo, which having rotten fell on him.